Method and Apparatus For Testing Heavy Oil Production Processes

ABSTRACT

There is disclosed a method of testing oil extraction processes including the steps of: 1) placing a sample to be tested in a sample holder which has a configurable temperature profile; 2) placing the sample holder in a pressure vessel; 3) increasing the pressure in the pressure vessel to simulate an over burden pressure; 4) configuring the temperature profile of the sample holder to match a desired temperature profile; 5) applying an oil extraction process to the sample; 6) measuring one or more parameters of the oil extraction process; 7) measuring the temperature of the sample to which the process is being applied; 8) configuring the sample holder to match the measured temperature profile. A device to test oil extraction processes on samples is disclosed. The device has a temperature configurable sample holder having sufficient temperature control to provide a desired heat profile to the sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser.No. 10/900476, filed on Jul. 28, 2004, the content of which is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates generally to the field of heavy oil or tar sandextraction, and more particularly to experimental techniques and methodsthat may be used to model temperature sensitive in situ extractionprocesses. Most particularly this invention relates to equipment andmethods to model and test, on a small scale, in situ extractionprocesses for heavy oil and tar sands.

BACKGROUND OF THE INVENTION

This invention relates generally to the extraction of heavy oil andbitumen. Heavy oils are crude oils, which have high specific gravity andviscosity and are therefore difficult to extract commercially becausethey do not readily flow. Tar sands are geological formations in whichheavy oil is trapped within a sand formation. Achieving in situseparation of the heavy oil from the sand is a well-known and difficultchallenge.

Currently steam is the dominant thermal fluid used for in situ recoveryof bitumen and heavy oil. Injected steam raises the temperature of thebitumen thereby reducing its viscosity and allowing it to flow moreeasily. Steam extraction is subject to a number of problems includinghigh heat losses, clay swelling problems, thief zones, water-oilemulsions, capillary surface tension effects, lack of confinement forshallower zones and disposal of large quantities of environmentallydamaging salt and organic acids as a consequence of boiler feed waterpurity requirements. By some estimates, with the best currentlyavailable technologies, only 10% of the original bitumen resource in theAthabasca tar sands are economic to extract.

Thermal recovery processes, using steam, also require large amounts offuel to be burned to produce the steam and can emit enormous amounts ofgreenhouse gases such as carbon dioxide. Estimates published by NaturalResources Canada¹ show CO2 emissions of about 70 kg/bbl for bitumenproduction and a total of about 120 kg/bbl for synthetic crude (i.e.upgraded bitumen usually derived from surface mined bitumen). ¹ Canada'sEmissions Outlook: an Update, December 1999, Annex B, pg B-6, Availableat www.nrcan.gc.ca/es/ceo/update.htm

Recent estimates released by the Alberta Energy Utilities Board² and theCanadian Association of Petroleum Producers³, predict that bitumen (andsynthetic crude) production rates will be 2 to 2.6 million bbl/day ofbitumen by 2010. This level of bitumen production will produce at least140 million kilograms (=70×2 million) of CO2 emissions per day (i.e.300,000,000 to 700,000,000 lbs CO2 per day depending on fuel source andthe proportion of in situ vs synthetic crude production). ² Alberta'sReserves 2000 and Supply/Demand outlook 2001-2010, Alberta EnergyUtilities Board³ Canada's Oil Sands Development delivered by EricNewell, Chairman & CEO, Syncrude Canada. Available athttp://www.capp.ca/

Solvent extraction processes have been proposed as an alternative tosteam extraction processes. One such process is the N-Solv process(Canadian Patent Applications, 2299790, 2351148, 2374115). However, thephysical chemistry of the bitumen extraction in solvent gravity drainageprocesses is not very well understood or characterized. For example,Dunn⁴ et al first reported in 1989, that for a cold solvent extractionprocess the measured CO2 diffusion rates in the tar sands were a factorof 460 times higher than the theoretically predicted values. Thisunexpected result has been observed and reported by many subsequentresearchers using a variety of different solvents and crude oil samplesand yet the underlying physical mechanism is still not understood. ⁴Dunn, Nenniger and Rajan, A Study of Bitumen Recovery by GravityDrainage Using Low Temperature Soluble Gas Injection, Canadian JournalOf Chemical Engineering Vol 67, December 1989, pg 985

Several computer models have been developed to predict the extractionrates for gravity drainage bitumen extraction using solvent. However,these computer models do not appear to be capable of accuratelydescribing the in situ processes. One potential problem of such modelsis a lack of spatial resolution because the models are typically far toocoarse to accurately model the solvent concentration gradients. Forexample, lab studies by Fisher⁵ have revealed that the solvent-bitumeninterface is only a couple of millimeters thick. An appropriategridblock size to accurately model in situ concentration gradientsshould be perhaps 10 times smaller (i.e. 100-200 microns). With typicalgrid block sizes of ˜0.5 m used in computer modeled reservoirsimulations (see Nghiem⁶), the calculated concentration gradients in thereservoir simulators are about 500 times smaller than values actuallymeasured in the laboratory tests. For a 3D computer model with anappropriate spatial resolution the number of calculations increases by afactor of 5000³ (=125,000,000,000), which increases the model run timefor a given scenario to an unworkable duration. Since the solventconcentration gradient provides the primary driving force for solventpenetration and extraction, existing computer models have a significantproblem in accurately representing the process. ⁵ Fisher et al, ‘Use ofMagnetic Resonance Imaging and Advanced Image Analysis as a Tool toExtract Information from a 2D Physical Model of the Vapex Process”,Society of Petroleum Engineers Paper 59330, April, 2000⁶ Nghiem et al“Modelling Asphaltene Precipitation and Dispersive Mixing in the VapexProcess, SPE paper 66361, FIG. 2

As noted earlier, researchers consistently measure bitumen extractionrates with solvents that are much higher than expected. Thus, webelieve, it is necessary to use physical models (i.e. experiments) toobtain meaningful data on bitumen yield, extraction rate and bitumenquality. Furthermore, until the details of the solvent extractionmechanism are better understood, we believe that it is unrealistic toexpect credible predictions from the existing computer models.

Due to the complexity of physical processes (combined heat, mass andmomentum transfer with simultaneous asphaltene precipitation) it may notbe possible to ever develop a fully rigorous theoretical computer model.However, empirical models can be developed that are both accurate anduseful. Such empirical models typically require data from a large numberof representative physical experiments to be able to develop parametricsensitivities to process variables. This type of experimentation isexpensive and time consuming, but has provided the basis for many (ifnot most) useful chemical engineering processes. However, it isnecessary to conduct physical experiments which accurately represent thespecific physical processes of interest and it is necessary that thesame be accurately measured before a meaningful empirical model can bedeveloped.

The prior art experimental apparatuses and techniques in the tar sandextraction field are generally intended to simulate a small twodimensional slice of a reservoir. These experiments are typicallyconducted in a thin walled rectangular can that is packed with tar sand(see Dunn⁴ and Frauenfeld⁷) with physical properties relevant to thereservoir of interest. A simulated injector well is usually locatedabove a simulated producer well at one end of the can. The can is placedwithin a pressure vessel and external pressure is applied to the can tomimic the overburden stresses appropriate to that reservoir. ⁷Frauenfeld et al., Evaluation of Partly miscible Processes for AlbertaHeavy Oil Reservoirs, Journal of Canadian Petroleum Technology Vol 37 no4, 1998

Tar sand extraction processes are typically based on some type ofthermal effect and therefore appropriate consideration of thermaleffects in the experiments is important. Two aspects of thermal behaviorhave been identified that can greatly affect the experimental modeling.First, there is a need to mimic to temperature profiles and temperaturegradients within the tar sand which arise due to the thermalcharacteristics of the reservoir extraction process. Second, heat may belost through the conductive nature of the can or sample holder of atypical experimental apparatus with the consequent distortion of thetemperature profiles within the sandpack. Such heat loss is referred toas parasitic heat losses,

Parasitic heat loss is an ongoing problem with all thermal gravitydrainage experiments. Typically, SAGD researchers have used thedimensional scaling criteria of Butler, to work around this problem.Butler's scaling criteria predicts that by increasing the tar sandpermeability, the time scale can be compressed (i.e. 1 hour ofexperimental time corresponds to 1 year of field time). Thus, scaledexperiments minimize the impact of parasitic heat losses by greatlyreducing the experimental time. Butler has used the analogy between heattransfer and mass transfer to develop similar scaling criteria forsolvent processes⁸. However, as noted above, the solvent extractionmechanism is not well understood so the scaling assumptions of Butler'ssolvent model are in doubt. Thus a different approach from the prior artscaling assumptions of Butler is needed. ⁸ Butler et al, A New Process(Vapex) for Recovering Heavy Oils by Using Hot Water and HydrocarbonVapour, Journal of Canadian Petroleum Engineering January-February 1991,vol 30, No. 1

FIG. 1 is based on prior art and illustrates the problem that thepresent invention seeks to address. FIG. 1 shows transient (onedimensional) temperature profiles at different times for a section oftar sand initially at 8 C when one edge is suddenly heated to 50 C. InFIG. 1 zero on the x-axis represents a bitumen interface. FIG. 1 showsthe temperature profiles along a 60 cm section of tar sand initially at8 C after time intervals of 1 minute, 2 hours, one day, three days andseven days from when one edge is suddenly heated to 50 C. The physicalproperties of the tar sand and the temperature profiles were calculatedusing the data and formulas presented by Birrell⁹. FIG. 1 also shows atemperature profile expected for a continuous bitumen extraction processtaking place in 8 C tar sand with the interface heated to 50 C and anassumed extraction rate of 5 cm/day again using the formulas presentedby Birrell⁹. This latter temperature profile is referred to as aquasi-steady state profile, as it is not expected to change further overtime (since the x-axis origin is the bitumen interface). FIG. 1 showsthat it takes a period of seven days for a sample sandpack to acquire asmooth temperature profile (assuming no parasitic heat losses out thesides of the apparatus), but even then it does not have the sametemperature profile predicted for “quasi-steady state” operation. Thisfigure shows that accurate process measurements cannot be made until thetemperature profile no longer is changing over time, which even in asmall sample can take a very long time to be established. ⁹ Birrell,Heat Transfer Ahead of a SAGD Steam Chamber: A Study of ThermocoupleData From Phase B of the Underground Test Facility (Dover Project),Journal of Canadian Petroleum Technology, March 2003

At quasi-steady state conditions, the bitumen interface moves with aconstant velocity and the solvent condenses at a constant ratedetermined by the temperature gradient (i.e. conduction heat loss) atthe bitumen interface. If we consider the temperature gradient at thebitumen interface, (i.e. slope of the temperature profile at x=0), thenFIG. 1 shows that temperature gradient is far too high, and consequentlythe solvent condensation rate will be substantially in error for thefirst seven days of an experiment.

In addition to the problem of achieving quasi-steady state temperatureprofiles, the parasitic heat losses can be 10-100 times larger than theexpected heat delivery rate. If solvent condensation is the only sourceof heat in the experiment, then these parasitic heat losses result insolvent condensation rates 10-100 times too high. High solventcondensation rates are undesirable and can lead to a host ofcomplications including flooding of the vapour chamber with liquid anddestabilization of asphaltenes. Thus, it is important to minimize theparasitic heat losses and correctly approximate the quasi steady-statetemperature profiles for an accurate simulation to occur.

Thus, in the absence of appropriate scaling assumptions, which shortenthe time of the physical experiments, real time experiments arerequired. In real time experiments, temperature effects become of muchgreater concern and represent significant limitations on experimentalaccuracy. What is needed is an experimental technique and apparatus inwhich the parasitic heat losses and temperature profiles are controlledin a way that permits measurements to be made which accurately reflectin situ circumstances, without an undue amount of time being required.The data generated by such techniques can then be used to developaccurate empirical models.

BRIEF SUMMARY OF THE INVENTION

The present invention teaches method and apparatus for testing solventextraction processes for the tar sands. Such testing is desirable todetermine the impact of changes in process conditions on the bitumenyield, extraction rate and the degree of upgrading for among otherthings, heated solvent processes. An object of the present invention isto permit real time testing to occur, without needing to run eachexperiment for many days before experimental sampling can even begin.

What is desired is a means to configure temperature profiles withintesting samples to simulate predetermined in situ temperature profiles.In this respect predetermined temperature profiles can be selected to,for example, minimize parasitic heat losses and to also minimize theamount of time required to establish the preferred temperature profiles.Thus an object of the present invention is to permit relatively quickand accurate measurements to be made of solvent extraction processes.

An aspect of the present invention is to provide a method and apparatusthat establishes temperature boundary conditions for an experimentalsample undergoing a proposed extraction process, which properly mimic anin situ section of the reservoir. Thus, rather than using a scalingassumption to overcome such temperature sensitivities as in the priorart, the present invention provides a method of configuring atemperature profile of a sample being tested to simulate its in situproperties.

In one preferred embodiment the present invention provides a heatconfigurable sample holder, for holding the samples during the course ofthe experiment. The sample holder may, for example, be provided with anouter shell that incorporates individually controllable and localizedheaters, each of which has thermal contact through the sample holderwith the sample. Each of the heaters can be in the form of an electricalresistor, which is periodically energized to supply heat and atemperature sensor to measure the heater temperature. Each heater ispreferably mounted on a thermally conductive base, which may take theform of a small tile. Each tile has sufficient thermal mass that thetemperature fluctuation through a duty cycle is appropriate for theaccuracy and precision of the temperature sensor. The tiles have highthermal conductivity to individually achieve a uniform temperature, butmost preferably are thermally insulated from any adjacent tiles so thattemperature gradients along the sidewall of the sample holder can bemaintained without excessive heat loss. Thus the present inventionprovides a heat configurable sample holder, in which the temperatureprofile can be set according to any predetermined pattern, where theresolution of the temperature pattern is determined by the size of theindividual tiles or conductive heater bases.

The present invention also provides for an array of temperature sensorsplaced within the tar sand sample being tested which produce an outputenabling the temperature profile of the sample to be accuratelymeasured. The sensed temperature profile is then processed through amapping algorithm to determine a smoothed temperature profile within thesand. This temperature profile is used to establish the desiredtemperature for each individual tile. Thus an object of the presentinvention is to provide a control system which supplies an appropriateamount of power to the individual heater elements to allow the sampleholder temperature profile to match the local internal sample sandtemperature profile and thereby minimize any parasitic heat losses.

Therefore, according to an aspect of the present invention there isprovided a method of testing, in a lab, an in situ extraction processcomprising the steps of:

-   -   placing a sample to be tested in a sample holder having a        configurable temperature profile;    -   placing the sample holder in a pressure vessel;    -   increasing the pressure in the pressure vessel to simulate an        overburden pressure;    -   configuring the temperature profile of said sample holder to        match a desired temperature profile,    -   passing a solvent into said sample, and    -   measuring one or more parameters of said oil extraction process.

In another aspect the present invention provides for:

configuring a temperature profile of said sample holder to match ameasured internal temperature profile of a sample arising during theapplication of an extraction process to said sample.

According to yet another aspect there is provided a testing device toconduct oil extraction process experiments on a sample to be tested,said testing device comprising a temperature configurable sample holderto provide a desired temperature profile to said sample.

The concepts taught in this patent may also have application inenhancing recovery of both heavy oil and less viscous oils.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example only, to preferredembodiments of the invention as illustrated in the accompanying drawingsand in which:

FIG. 1 shows the (one dimensional) temperature profiles along a 60 cmsection of tar sand initially at 8 C after time intervals of 1 minute, 2hours, one day, three days and ten days from when one edge is suddenlyheated to 50 C;

FIG. 2 a shows a schematic of a section of the heater tile array forconfiguring temperatures according to the present invention;

FIG. 2 b shows a side view of the heater tile array of FIG. 2 a;

FIG. 3 shows a more detailed view of sample holder having a samplesandpack and the placement of in situ temperatures sensors according tothe present invention;

FIG. 4 shows a schematic of a power circuit to energize individual tilesaccording to the present invention;

FIG. 5 shows a schematic of a data acquisition system and the meanswhereby a particular heater element interacts with the data acquisitionsystem;

FIG. 6 outlines the temperature control algorithm during startup for thepresent invention;

FIG. 7 outlines a tile temperature control algorithm during operationafter the solvent vapour is injected into the sample sandpack; and

FIG. 8 compares the target “quasi-steady state” temperature profileswithin a sample sandpack to predicted temperature profiles along a sidewall of a sample holder of the present invention. Temperature profilesare shown at startup and again after 4 days, assuming an interfacevelocity of 5 cm/day.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is calculated from the prior art as described in the backgroundand illustrates the problems that the present invention seeks toaddress. FIG. 1 shows transient (one dimensional) temperature profilesat different times for a section of tar sand initially at 8 C when oneedge is suddenly heated to 50 C, for example by a condensing solventprocess. FIG. 1 also shows a “quasi-steady state” temperature profilefor a bitumen extraction process taking place in 8 C tar sand with theinterface heated to 50 C and an extraction rate of 5 cm/day. A physicalmodel experiment must reproduce the appropriate “quasi-steady state”temperature profile, to accurately model in situ processes and thus togenerate meaningful process test data. It will be understood by thoseskilled in the art that FIG. 1 only shows one-dimensional temperatureprofiles rather than the full 2D temperature map for the sake ofclarity.

At “quasi-steady state” the sample has attained a temperature profilethat mimics an in situ profile. In FIG. 1 the temperature profile of thequasi steady state curve is of constant shape, and even if the processcontinues, the shape will not change. The origin represents a bitumeninterface, where the solvent vapour is condensing, and in absolute termsthis interface will be moving at an estimated speed corresponding to therate of extraction. However, even as the interface moves through thesample (mimicking movement through the reservoir in an actualextraction) the shape of the temperature profile extending out from theinterface remains the same. In this specification the term “quasi-steadystate” identifies a sample condition that will permit process testing tobegin with meaningful measurements of process parameters being possible.Process parameters means any measurable aspect of a process that helpsin defining the value properties or efficacy of a process, such asextraction rate, bitumen quality or the like. The term sample shall meanan actual sample of an in situ oil bearing formation, or a made upsample which is provided with certain characteristics to mimic the insitu reservoir conditions, or any other configuration of materials whichmay be used to provide tests on the process of interest. Typically, asample will comprise a graded sand which is water wetted and oilsaturated in a known manner.

FIG. 2 shows a schematic of a section 10 of a temperature configurablesample holder according to the present invention. The section 10 shows aplurality of heater elements 14 embedded into heat conductive tiles 16.As shown the heating array may take the form of 2×2 cm tiles on a 2.5 cmpitch. Each tile 16 is shown with an embedded resistor heater element 14that is energized as needed to control the temperature of the tile 16.Although one heater per tile is shown, it will be understood that thepresent invention comprehends that more heaters may be added if neededto provide the desired amount of heat. However, one per tile ispreferred. Each tile 16 is also equipped with a temperature sensor 15,which is preferred to be a type T calibrated thermocouple or the like.

The most preferred form of heater element 14 is a resistor heaterelement. A 100 ohm wirewound resistor provides adequate results. Thetype and properties of the heater can be varied, but what is needed is aheater power matched to a tile size to ensure that the local temperaturewithin the apparatus can be matched by the tile temperature. For thepurposes of the invention the resistor may be operated at power levelsexceeding its' nominal rating. Destructive tests have shown that this isfeasible, if the duration of the heating time is limited and theresistor is adequately thermally potted to limit temperature rise withinthe resistor. Consequently in the preferred form of the inventionillustrated the resistor is placed within the tile and potted with athermal conductive epoxy or the like such as Supertherm 2005manufactured by Tra-Con Inc of Bedford Mass. Other configurations ofheater element and tile combinations, such as surface mounted heatersthat provide the advantages of a temperature configurable sample holderare also comprehended.

The tiles 16 are shown mounted in an insulating matrix 20, made from,for example, silicone rubber or the like. The tiles are separated by agap of, for example, 5 mm which is large enough to reduce the heattransfer from one tile to the next but small enough to avoid excessivetemperature drop (sag) between adjacent tiles. In some cases it isdesirable to reduce the contact area of the tile 16 with the steel wall32. Reduced contact area reduces the amount of conduction heat fluxalong the steel wall 32 without increasing the gap between the tiles. Wecan obtain the reduced contact area with a “knob” profile 17 at thecontacting surface of the tile. The knob can be any convenient shape.Conventional wiring (not shown) connects the heater elements to anappropriate power source. Although any number of tiles may be used, itis estimated that 1024 tiles on a 2.5 cm pitch is sufficient tocompletely enclose a sample sandpack that is 32 cm high 62 cm long and12 cm wide (i.e. 13×25×5 tiles). While it is preferred to make the arrayas regular as possible, various openings may be required in the array toaccommodate thermocouple penetrations and whatever feed and drain portsthat may be needed.

FIG. 3 shows a more detailed isometric sectional view of the both thesandpack 28 and tile assembly. In FIG. 3, the sand pack 28 hastemperature sensing thermocouples 30 which are preferentially placed ona uniform spacing (i.e. 5 cm spacing). Between the sand pack 28 and thewall of the sample holder 32 is a rubber liner 34 or the like to smooththe adjacent tile temperatures out so that the step profile of the tilesmore nearly approximates the desired temperature profile of the sandpack28. The liner 34 also helps to dampen out fluctuations arising from thepower duty cycle. The layer of heater tiles is immediately outside thewall 32 and is physically clamped to the wall 32 to provide good thermalcontact between the tile assembly and the wall. This thermal contact isimportant to ensure that each tile can determine the local temperatureof the side wall 32 of the sample holder. Beyond the tiles are severalexternal layers which include the packaging 35 (wiring and mounting forthe tiles) as well as insulation 36 to reduce the heat deliveryrequirement of the tiles.

The tiles are preferably made of a high conductivity material such asaluminum or copper or the like, so they will individually maintain afairly uniform temperature across an individual tile. The smoothtemperature profile in the tar sand undergoing stimulation is thusapproximated by a sample holder temperature profile having a number ofsteps, each step representing a different tile. It will be understood bythose skilled in the art that the quality of the approximation dependson the resolution (i.e. tile size). Therefore the more numerous andsmaller the individual tiles, the more exactly the temperature profileto the sand pack 28 can be matched. A reasonable match is required toensure reasonably accurate experimental results. Furthermore, theindividual tiles may or may not be continuously energized so that theirtemperature may fluctuate slightly through a duty cycle. Providing liner34, which has some thermal resistance, mitigates these sources of error.By placing it on the inside of the sample holder it will act to dampenout the duty cycle temperature fluctuations and also smooth out the tiletemperatures across the assembly.

It can now be appreciated that during any experimental run thetemperature of each tile can be set to any desired temperature. This hastwo important advantages. Firstly, the desired in situ temperaturegradients can be externally imposed on the tar sand sample before thesolvent is introduced or the process experiment otherwise begun. Then,when the actual process testing is started, for example by injecting thesolvent into the sample tar sand pack, the individual tile setpoints canbe determined by mapping the internal temperatures within the tar sandas described below. This strategy allows the experiment to start closeto the desired “quasi-steady state” temperature profile and therebyminimize the duration of the thermal transient period. This strategyprovides a substantial time/cost savings and greatly improves theusefulness of the data since realistic solvent/oil ratios can beobtained right from the beginning of the experiment.

In addition, once the process has begun, and heat is being supplied tothe sample by means of the process being tested, appropriate thermalboundary conditions can be provided by the temperature configurablesample holder of the present invention. It is preferred to use thetemperature measured at the closest adjacent thermocouples 30 within thesand pack 28 as the basis for calculating the tile setpoint temperature.Temperature profiles in a heated gravity drainage process have beenpreviously measured (Birrell⁹) and according to the present invention insitu temperature profiles can be readily interpolated or extrapolatedfrom an array of temperature sensors in the sample. Interpolation and/orextrapolation of these curves together with the location of theindividual tile determine the desired temperature for a particular tile.This mapping is most convenient if the thermocouple spacing within thetar sand pack is a simple multiple of the tile spacing. For example,with 5 cm spacing on the thermocouples it is most convenient to havetiles on a 2.5 cm pitch.

FIG. 4 shows a power circuit 40 to energize the individual tiles. In apreferred embodiment the power is delivered by a 24 volt 8 Amp DC PowerSupply 42. The power is dissipated in a 100 ohm resistor 44. Thus, eachtile is energized with approximately 6 watts of power. As each tileincludes a temperature sensor, the control system will apply poweraccording to a difference between the desired tile temperature and theactual tile temperature. The size of the difference will determine thelength of time that the power is applied to any individual tiles. Anadequate configuration is for a ground connection multiplexer or “drainmultiplexer” 46 to cycle through each of the 32 columns in the preferredtile array with a 1 second dwell time for each tile column in the array.

An example arrangement for the drain multiplexer 46 is to use twodigital switch banks 48. Adequate results can be obtained from NationalInstrument Field Point Digital Switch Banks (each having 16 softwareprogrammable switches) part number FP-DO-401 to drive 32 individual 8amp rated relays 38. For such a mechanical relay arrangement, it ispreferential that all 32-power controller switches 39 are open circuit(i.e. there is no current flow) during the short time interval when thedrain multiplexer switches from one column to the next.

Thus, in this configuration a particular tile will cool continuouslyduring 31 seconds of the cycle and will be energized during the finalsecond of the 32-second cycle in order to achieve its targettemperature. The maximum power output of this particular configurationis about 180 watts. Other configurations and cycle times arecomprehended by the present invention, but the foregoing yieldssatisfactory results.

The output power controller 41 regulates power delivery to each of 32individual tiles by controlling a length of time that each tile isenergized by the DC supply. Again two Field Point Digital Switch Banks43, can be used to actuate a total of 32 power control relays 39. Forexample, if 3 joules of energy are required for a particular tile thenthe tile would only be energized for 0.5 seconds. The combination ofpower controller, drain multiplexer and the individual diodes 45associated with each power resistor avoids the problem of parallelcurrent paths thereby ensuring that the correct tiles is addressed andindividually energized at the appropriate level. This arrangement isparticularly convenient, because it allows a common wire to energize allthe tiles in a particular row and a common drain wire to return currentto ground for a particular column. The arrangement described canuniquely address and deliver power to 1024 individual tiles (i.e. =32columns×32 rows).

A large cost is associated with providing individual power supplies andcontrollers for each heater tile. The preferred configuration uses onepower supply and an appropriate arrangement involving digital switchesand diodes to individually and uniquely address a large number of tiles.The present invention therefore comprehends using the same to uniquelyaddress and energize individual tiles in a matrix consisting of 1024tiles via 32 individual power switches 39, a resistor 44 and diode 45pair on each tile, and one 32 channel drain multiplexer 48 whichconnects to ground.

With experiments conducted in pressure vessels, there is always asafety/reliability concern with electrical feedthroughs through the wallof a pressure vessel. Although feedthroughs are well known and commonlyused, they represent a possible leak path and present a risk ofcatastrophic failure. Thus, it is desirable to minimize the use ofpressure wall electrical feedthroughs. For example, with 1024 tilesthere would typically be 2048 thermocouple wires that would have to passthrough the wall of the pressure vessel. However, the preferredconfiguration of the present invention is to place most of theelectronics (multiplexers, digital switches, relays, data acquisioncards, power supplies, plc's etc) within the pressure vessel so theyoperate at elevated pressure and then to communicate to an externalcomputer via a single high-speed connection like an Ethernet link. Thisis outside the nominal operating specifications of some components butpressure tests have demonstrated that reliable operation can beachieved. This simplifies the design and greatly increases mechanicalreliability. The present invention also comprehends using wireless,optical or other signal communication that does not require apenetration through the wall of pressure vessel.

FIG. 5 shows a schematic of a data acquisition system 50 to address andmeasure a temperature of each individual tile 16. As previously noted,each tile has an individual temperature sensor 15. Preferentially thesensors 15 are type T thermocouples or the like that have sufficientsensitivity and accuracy. The sensors will be calibrated in situ withthe appropriate wiring in a known manner. Each thermocouple is connectedto an input multiplexer 52. Each row of tiles is connected to a commonmultiplexer 52. Input from the control system controls the switching ofthe multiplexers 52 to selective read temperatures in a particularcolumn of tiles. Further input from the control system controls theswitching of the multiplexers 54 to select the appropriate row of tilesfor measurement by the data acquisition system 58. In this way, the dataacquisition system can address each tile individually. Unfortunately,there is no easy arrangement to share common wires, so 2048 individualwires 56 are required to measure the temperatures of 1024 tiles. Forclarity, in FIG. 5, each single line 56 actually represents twothermocouple leads. The multiplexers 52, 54 are ADG732 from AnalogDevices and are mounted on small printed circuit boards (PCB) in orderto provide a good mechanical for support for the wire terminations.

Similar to the energizing of the heater tiles, a large cost ispotentially associated with providing individual data acquisitionchannels for each thermocouple. The present invention provides anefficient configuration since the thermocouples for each tile (i.e. 1024thermocouples) are connected through a series of multiplexers to a32-channel data acquisition system. These multiplexers provide a meansto uniquely address each individual thermocouple as explained above.

Cold junction error could be introduced into the thermocouple readingsby the wire connections. To minimize this type of error it is desirableto make the PCBs small and place them in a well-ventilated location sothe PCB's are effectively isothermal, thereby canceling out any coldjunction errors. Furthermore, it is important to use the appropriatethermocouple lead wire 60 for all subsequent connections back to thedata acquisition system Again for clarity, each thermocouple lead wire60 actually represents two thermocouple leads.

FIG. 6 depicts a startup temperature control algorithm. Good resultshave been obtained from software coded in National instruments Labviewprogramming language downloaded into a National Instruments Field Pointcontroller At start up, the present invention is able to configure adesired temperature profile in the sample holder at a given expected(either calculated or estimated) Quasi-Steady State (QSS) temperatureprofile.

Being able to directly apply this temperature profile to configure theprofile of the sample sandpack greatly reduces the length of time takento get to this condition.

According to the present invention an estimate is made of the bitumeninterface velocity in order to calculate the QSS. However, this may wellbe one of the parameters being determined by the experiment. Where theextraction rate is not known beforehand (an arbitrarily assumption of 5cm/day was used in FIG. 1), an estimate for the QSS can be made and asthe experiment proceeds the actual bitumen interface velocity isdetermined. The length of any transient period between start up andachieving QSS will depend on the accuracy of the first estimate.

Thus, FIG. 6 shows the following steps. At 100, determine the expectedQSS profile. At 102, map the individual tiles onto the QSS grid todetermine the desired temperatures for the tiles. At 104, measure theactual tile temperature and then calculate the appropriate amount ofpower that should be delivered to the tile to reach the desiredtemperature. At 106, energize the heater on the tile to deliver theappropriate amount of power. At 108 the sandpack temperature ismeasured. At 110 the sandpack temperature is compared to the desiredtemperature. At 112 the cycle is continued until the tile temperatureand the sandpack temperatures match the QSS target. This may takebetween 4 and 24 hours depending on the size of the sandpack and theexterior insulation. When the QSS profile is achieved then the processexperimentation can proceed and, for example, solvent can be introducedinto the sandpack 114.

According to the present invention the 2D slice of the reservoir thatthe experiment simulates should have no heat loss through the sidewalls,so the two sidewalls should be perfectly adiabatic. Thus, in addition toreducing the time to achieve QSS, the present invention eliminatesparasitic heat losses which otherwise can distort the experimentalresults. Eliminating parasitic heat losses does not mean perfectinsulation. To properly mimic the in situ conditions also requires acontrolled amount of heat loss or flux, through the top, bottom and endwalls of the sample holder to represent the temperature gradients andheat fluxes that would extend beyond the can into the surrounding“virtual” tar sand matrix. For example if we refer to FIG. 1 it shows,for a quasi steady-state profile, a temperature gradient occurs at 0.6 m(i.e. the end of the can). Controlled heat loss at the top bottom andend of the can is provided by accounting for the insulating quality ofthe liner and then calculating the appropriate temperatures forindividual tiles to match the heat fluxes necessary to simulate theexternal temperature gradients. For example, since the thermalconductivity of silicone rubber is about 10% of that of typical tarsand, a rubber liner thickness inside the can of 2.5 mm has the sameheat loss characteristics as a tar sand layer having a thickness of 2.5cm. This provides a simple and convenient way to calculate theappropriate desired tile temperatures at the top, bottom and end of thecan needed to match the heat flux boundary conditions. Using theequivalent “tar sand” distance of the rubber liner extrapolating from asmoothed sandpack temperature grid the appropriate desired tiletemperatures can be found for the top, bottom and end walls.

FIG. 7 shows the temperature control algorithm while in the midst ofconducting an actual process trial. Heated solvent vapour is beinginjected into the sandpack causing solvent diluted bitumen to drain fromthe sandpack. During this process the tile setpoint temperatures aredetermined by the measured internal temperatures within the sandpackinstead of the estimated QSS temperature grid. FIG. 7 shows that thecontrol system algorithm cycles through the following steps. At 200,measure sandpack temperature, at 202 calculate smoothed 2D temperaturegrid for the sandpack. At 204 map the tiles onto the sandpacktemperature grid to determine the setpoint temperature for individualtiles. At 206 measure the actual tile temperature and calculate theappropriate control action. And finally, at 208 energize the tile tosupply the required amount of heat.

For the 32×32 heater tile matrix described above, the individual heatertiles are energized for one second out of 32. The temperature dropduring the 31 seconds of cooling is determined by the heat loss (i.e.conduction heat loss along the side of the can, insulation+exteriortemperature and by the thermal inertia of the tile). The magnitude ofany temperature “bounce” can be reduced by increasing the heat capacityof the tile (i.e. the tile thickness), increasing the externaltemperature, or increasing the insulation. Referring to FIG. 1, we cansee that for an experiment at 50 C the QSS indicates that the lowesttemperature is about 33 C at 60 cm from the interface. Thus a minimumexterior temperature of about 25 C is likely required (to allow 33 Cwith heat conduction taking place along the side walls). With areasonable amount of insulation the cooling rate of a tile at 50 C is0.01 C/second, so the tile temperature will drop about 0.3C in a 30second cycle. To obtain the most accurate tile temperature measurementfor control, it is preferred to measure its temperature just prior toapplying power (i.e. at 31 seconds into the cycle in the example). Withthis configuration the tile temperature typically is within 0.2 C of thetarget setpoint temperature.

FIG. 8 compares the expected temperature profiles within the tar sand(i.e. QSS profiles) to the temperature profiles achieved along the sidewall by the present invention. Profiles are shown at startup and againat 4 days into an experiment assuming an interface velocity of 5 cm/day.The tiles match the temperature profile but also introduce a temperatureerror due to the step changes in temperature between adjacent tiles.FIG. 8 shows that the maximum temperature error (i.e. the differencebetween the tar sand and the wall temperature) is about 0.3 C. For arubber liner of ¼″, this is equivalent to a parasitic heat loss near thebitumen interface less than 1% of the target heat delivery rate.Including a ±0.2 C “bounce” from the duty cycle of the control system,the total heat loss error should be within a few percent of the ideal(i.e. in situ reservoir) case. By comparison a highly insulatedconfiguration which is not configurable as is the present invention willstill have parasitic heat losses 10 to 100 times larger than the totaltarget heat delivery rate, making experimental results all butmeaningless.

It can now be understood how the present invention may be used todetermine a true bitumen extraction rate. There are several criteriathat can be used. First, the location of any vapour chamber that formscan be measured by means of the sandpack thermocouples. The temperatureprofile will indicate a position of the bitumen interface. By trackingits position over time an extraction rate can be determined. A solventdelivery rate (i.e. condensation rate) can also be measured and used todetermine if the heat delivery rate is consistent with the displacementof the bitumen interface. (i.e. does the heat balance close?). Closingthe heat balance verifies that a true measurement was made that is notdistorted by temperature transients. We can estimate bitumen yield (i.e.the rate of bitumen recovery) by comparing actual bitumen production(i.e. after removing the solvent) to the interface position. All ofthese may be referred to as parameters of the extraction process. Theforegoing is not intended to be restrictive and it will be realized thatother parameters can also be measured to help analyze the efficacy ofvarious production techniques.

It will be appreciated by those skilled in the art that while theforegoing description relates to preferred embodiments of the inventionvarious alterations and modifications are possible without departingfrom the broad scope of the appended claims. For example, while theforegoing discussions are centered on a condensing solvent extractionprocess, the present method and apparatus could be used on other typesof thermally based in situ recovery processes, such as being used tostudy bitumen extraction in SAGD type processes. The components (i.e.power resistors, wiring etc) would have to be appropriately sized tooperate higher temperatures which are typical of such SAGD processes. Inaddition there also are processes that propose to use solvents mixedinto the steam that would be good candidates for using the presentinvention, since the prior art scaling criteria for any solventprocesses is in doubt.

1. A method of testing an oil extraction process comprising the stepsof: placing a sample to be tested in a sample holder having aconfigurable temperature profile; placing the sample holder in apressure vessel; increasing the pressure in the pressure vessel tosimulate an overburden pressure; configuring the temperature profile ofsaid sample holder to match a desired temperature profile; applying saidheavy oil extraction process to said sample; and measuring one or moreparameters of said heavy oil extraction process.
 2. A method of testingan oil extraction process as claimed in claim 1, further including thestep measuring one or more temperatures at one or more locations withinsaid sample and configuring a temperature profile of said sample holderbased on said measured temperatures.
 3. A method of testing an oilextraction process as claimed in claim 1, further including the step ofmeasuring said sample temperatures over time and adjusting over timesaid heat configurable sample holder temperatures.
 4. A method oftesting an oil extraction process as claimed in claim 1, wherein saidstep of configuring the temperature profile of said sample holdercomprises estimating a desired temperature profile and energizing saidconfigurable temperature profile sample holder for a sufficient amountof time to permit said sample to substantially attain said desiredtemperature profile.
 5. A method of testing an oil extraction process asclaimed in claim 1, wherein said heavy oil extraction process includes astep of injecting a solvent into said sample.
 6. A method of testing anoil extraction process as claimed in claim 1, wherein said step ofconfiguring said temperature of said sample holder comprising energizingone or more electrical heaters to a desired temperature.
 7. A method oftesting an oil extraction process as claimed in claim 6, furtherincluding the step of measuring a temperature of said heaters to permitthe energy to said heater to be adjusted to achieve said desiredtemperature.
 8. A method of testing an oil extraction process as claimedin claim 1, wherein said step of measuring said parameters comprisesmeasuring one or more of an extraction rate, bitumen yield or rate ofprogress of an extraction chamber interface.
 9. A method of testing anoil extraction process as claimed in claim 1, wherein said temperatureconfiguration of said sample holder permits an amount of heat fluxapproximately equal to an expected heat flux in a reservoir from whichsaid sample was obtained under process operating conditions.
 10. Amethod of testing an oil extraction process as claimed in claim 1,wherein the temperature of the pressure chamber is set lower than alowest temperature of said sample to permit said expected heat flux tobe present during said testing.
 11. A method of testing oil recoveryprocesses on a sample in a sample holder, said method comprising:measuring an internal temperature profile of a sample upon which an oilrecovery process is being tested, and configuring a temperature profileof said sample holder to match said measured internal temperatureprofile.